1. Field of the Invention
The present invention relates to a magnetic disc apparatus and in particular, to a magnetic recording apparatus having a magneto-resistance effect element opposed to a magnetic recording medium for reading information.
2. Description of the Related Art
A magnetic disc apparatus can employ a magneto-resistance effect type thin film head utilizing the magneto-resistance effect and capable of obtaining a large reproduction output not depending on a velocity relative to a medium. In such a magnetic disc apparatus, rotation of a magnetic disc causes a slider to float above a disc surface and rotation of a carriage moves a reproduction head to a predetermined position on a magnetic disc, so that information can be read from the magnetic disc via the magneto-resistance effect element provided in the reproduction head,
That is, when magneto-resistance effect element (hereinafter, referred to as an MR element) is supplied a with a constant sense current and made to face a magnetic disc, resistance of the MR element is changed by a change of magnetic field, i.e., a change of magnetization direction in the magnetic disc (medium). The change of the magnetization direction is converted into a voltage change at both ends of the MR element, so as to obtain a reproduction output voltage corresponding to a resistance change ratio of the MR element, thus enabling reproduction of an information recorded on the magnetic disc according to the reproduction output voltage.
In the aforementioned reproduction method, the distance between the reproduction head and the magnetic disc is made as small as possible, so as to increase the magnetic field that can be sensed by the MR element and increase the reproduction output. This brings about various problems as follows.
That is, in the magnetic disc apparatus, when the MR element or other portion of the head is brought into contact with the magnetic disc and heat is generated by friction, the MR element changes its temperature and its resistance value. In this case, the voltage change cased by a change of the magnetization direction is overlapped with the voltage change caused by the temperature change to determine the reproduction output voltage change.
Moreover, when the MR element is in contact with a magnetic disc, they communicate with each other and the sense current to be supplied to the MR element may be temporarily shunted to the magnetic disc. This changes the voltage at the both ends of the MR element and this change is involved in the change of the reproduction voltage. Accordingly, an abnormal waveform is generated in the reproduction output. This increases the frequency of a reproduction error and may even disable reproduction, deteriorating the reliability of the apparatus.
As has been described above, an abnormal waveform generated when the MR element is brought into contact with the magnetic disc is caused by a temperature change or sense current shunting. The temperature change may be suppressed by making the surface of the magnetic disc more flat and smooth eliminating fine protrusions and the like from the surface, i.e., by mitigating the friction state with the MR element.
However, no effective countermeasure has been suggested to cope with the sense current shunting. For example, the MR element has a protection layer on its surface opposing to the magnetic disc so as to cope with friction. This protection layer also serves as an electrical insulation layer to a certain extent.
However, if the protection layer is too thin or worn out and incapable of obtaining a sufficient insulation effect, the sense current is shunted from the MR element to the magnetic disc, resulting in an abnormal waveform.